The present invention relates generally to a multi-channel signal synthesizer system providing a wide variety of complex signal waveforms, and, more particularly, relates to a four channel numerical digital synthesizer system providing one or more output signals having selectable waveform and modulation characteristics.
Most signal synthesizer systems provide precision waveforms, signals with frequency accuracy and resolution for test evaluation of electrical systems. For example, a signal channel synthesizer system can be synthesizer, function generator and sweep generator providing sine waves, square, triangle and ramp waveforms for use. As a synthesizer, the single channel system provides waveforms having precise frequency control. As a function generator, the synthesizer system provides a variety of waveforms including sine, square, triangle and ramp. As a sweep generator, the synthesizer can sweep over a range of frequencies. However, there is a high demand for much improved performance of the prior art synthesizer systems in spectral purity, phase noise and phase accuracy. Further more, it is desirable to provide the prior art synthesizer system with a variety of additional capabilities and functions.
Various types of digital frequency synthesizers are known in the art. U.S. Pat. No. 3,735,269 entitled "Digital Frequency Synthesizer" granted to Leland B. Jackson on May 22, 1973, discloses a digital frequency synthesizer which is programmable to provide desired frequency outputs. Jackson discloses a digital synthesizer which includes storage means such as a read-only-memory (ROM) in which digital values corresponding to digital samples of the desired output signal from the synthesizer are stored. These digital samples represent a predetermined waveform, such as a sine wave. In response to a digital signal representing a predetermined frequency output the storage means provides output signals corresponding to the digital values stored therein. The successively generated digital values are fed to a digital-to-analog convertor (DAC) which generates a step-type representation of the desired output signal. The output signal is then smoothed in a low pass filter to provide an output signal having the predetermined frequency and waveform. The synthesizer system of Jackson does not provide multi-channel capabilities nor does it provide selective modulation and waveform generation capabilities.
The main object of the present invention is to provide a multifunction digital frequency synthesizer which is easily programmable to provide complex output waveform signals from a variety of selectable fundamental waveforms.
Another object of the present invention is to provide such a multifunction digital frequency synthesizer system having multiple internal channels to provide frequency, amplitude, phase and pulse modulation of a single channel with selectable waveform or be summed at the output to provide a single complex output waveform.
A further object of the present invention is to provide such a digital frequency synthesizer which utilizes a single VLSI integrated circuit (IC) to achieve the direct digital synthesis, waveform generation, summation, multiplication, modulation and multiplexing functions to achieve a high level integration which results in an output signal having well-defined accuracy and exact repeatability at a low cost.